Method of making powdered material and the usage thereof



?atented July li t 3%2 MAWG row/p m MATE- arcane REAL AND THE USAGE THEREOF Alfred L. lBoegehold, Detroit, Mich, aesignor to General Motom Corporation, Detroit, Mich, a

corporation oi Delaware No Drawing. Application December 24, 1940, Serial No. 371,577 g 9 Chime.

This invention relates generally to the production of powdered alloy materials and to the use of the powder in the formation of sintered articles. Specifically, the invention has to do with the formation of prealloyed magnetic materials in powdered form, especially those of low coercive force, and to the usage of the powdered materials in the formation of sintered articles such as relay cores and the like.

One object of thisinvention is to provide improvements in a method of making a powdered magnetic material.

Another object-of the invention is to provide a convenient and practical method of forming a prealloyed magnetic material, particularly one of low coercive iorce;in the form of a powder which can be briquetted and slntered to form desired shapes.

It is also an object of the invention to provide a relatively brittle alloy material free of undesirable impurities, that may be comminuted or ground into the form of a fine powder, and which powder can be readily converted to a powdered material especially adapted for use in the formation of sintered relay cores and the like.

Still another object of the invention is to provide a convenient method of making a prealloyed low coervice force material of specific analysis and to the powder resulting from the method.

Other objects and advantages of the invention will become more apparent as the description proceeds.

In carrying 'out the method in accordance with the invention, I preferably provide a molten composition containing a small amount of caroon in addition to the alloying constituents necessary to provide the magnetic properties desired in the final powder. The purpose of the :arbon is to increase the brittleness of the ma- :erial when rapidly cooled so that it is easier to :omminute it to' the size of powder desired. The small amount of carbon also has the important effect of lowering the melting point of the mixmm and resulting in a more fluid composition. the powdered material containing carbon is then lecarburized to remove all or approximately all if the carbon to thus produce a powdered maerial having the magnetic properties desired.

In forming the powdered material containing :arbon in accordance with a preferred embodinent of the invention, the molten composition first atomized by flowing a molten stream hereof into a high velocity jet or jets of'water, Ir other fluid, to break it up into a large number and become harder and more brittle than where no carbon is present. The atomized particles are preferably produced in as brittle a condition as possible in order that they may be more readily comminuted by any suitable means to form a powdered material of the desired fineness. In powdering the material to the final size desired any suitable ball mill, pulverizer, crusher, or the like may be employed. The size of powder produced may vary considerably. Ordinarily it should practically all pass through a 100 mesh sieve and in practice it is preferred that about ground or pulverized to the desired powder size. I

In general, amounts or carbon as low peroximately 1% or even lower, have an effect on the fluidity of the molten composition and on the ease with which the atomized particles can be ground to a fine powder. The higher amounts of carbon increase are fluidity of the molten composition and greatly increase the ease with which the atomized particles can be ground to the size desired. It is at present preferred that about 2% or more of carbon be present in the molten composition.

The alloy powder containing the carbon is thereafter annealed in a decarburizing, non-oxidizing atmosphere to soften the same and reduce the carbon content thereof. .Preierably the decarburization is carried out to the point where very little carbon remains therein; for example to form an alloy powder containing .05% or less of carbon. Usually the decarburization is such as to provide a powder containing .03% carbon or less. Any suitable decarburizing, non-oxidizing atmosphere such as one containing moist hydrogen, for example, may be employed to carry out the decarburization. Temperatures of about 1400 F. to about 2000 F. may be used. A convenient method and apparatus for carrying out the decarburization is shown and described in the copending application of Robert N. Terry and Donald J. Henry, S. N. 361,400, filed October If rather fine particles which are rapidly cooled 16, 1940.

The present invention has application to making various alloy powders having magnetic properties, particularly alloys of low coercive force. Preferred compositions are those containing iron, nickel and molybdenum. For example, alloys composed largely of iron and nickel together and having a small amount of molybdenum have proven especially desirable in forming alloy powders of low coercive force. Ordinarily I prefer that the iron and nickel be present in approximately equal amounts. Generally, also, the molybdenum content is between 2.20 and 2.50% and the balance oi the alloy approximately equal amounts oi iron and nickel. In certain applications the molybdenum may be omitted and an alloy powder consisting essentially of iron and nickel be formed.

The following is a specific example 01, procedure in accordance with the invention. A molten composition containing 48% nickel, 2.42% molybdenum, about 2% carbon, and the balance iron pli's traces of non-essential impurities, was atomized and the atomized particles thereafter ground to a powder of a size such that it all passed a 150 mesh screen and about 85% passed through a 200 mesh screen. A similar composition without carbon is so tough that it is powdered with diiiiculty. The powder was then decarburized in a non-oxidizing atmosphere containing moist hydrogen until .03% carbon remained therein. A temperature of approximately 1900" F. was used. The decarburized powder was briquetted to form relay cores and the relay cores were thereafter sintered under non-oxidizing conditions. In some cases the sintered relay cores were annealed in hydrogen. Strong, homogeneous cores are produced in this manner. The pressures used in the briquetting operation are of the same order as those now employed in making articles by briquetting and sintering metal powders.

Various changes and modifications in the em-= bodiments of my invention described herein may be made without departing from the principles of my invention and I do not intend to limit the patent granted thereon except as necessitated by the prior art.

Iclaim:

1. The method 01' forming an alloy powder of low coercive iorce which comprises, providing a molten composition consisting of large amounts or each of nickel and iron and containing about 1 to 4% 06 carbon, said composition when substantially devoid of carbon being one of low coercive force, atomizing said molten composition and rapidly cooling the atomized particles to form comparatively hard and brittle alloy particles of rather small size, comminuting said hard and brittle alloy particles to form alloy powder particles of a size such that they will pass through a 100 mesh screen, and decarburizing said comminuted alloy powder to form an alloy powder of low coercive force composed of large amounts of each 01 nickel and iron and containing not more than .05% carbon.

2. The method of forming an alloy powder of low coercive force which comprises rapidly cooling to make it relatively hard and brittle, an alloy composition containing large amounts of each of nickel and iron and containing about 1 to 4% of carbon, said alloy com-position when substantially devoid of carbon being one of low coercive force, comminuting said alloy to produce powdered alloy particles of a fine size, and decarburizing the powdered alloy to produce an sesame alloy powder of low coercive force containing large amounts of each or nickel and iron and containing no more than about 135% of carbon.

3. A method of forming amagnetic alloy powder of low coercive force which comprises, providing a molten composition composed largely of iron and nickel and containing small amounts of molyb denum and carbon, atomizing said molten material and rapidly cooling the same to form comparatively hard and brittle alloy particles of rather small size, comminuting said brittle atomized alloy particles to form alloy powder particles of the desired size, and decarburizing said powder particles to form a low coercive force alloy powder composed essentially of iron, nickel and molybdenum.

4. The method of forming a magnetic alloy powder 01' low coercive force which comprises,

comminuting an alloy material containing large amounts of each of nickel and iron and containing a small amount of molybdenum and about 1 to 4% of carbon, to form alloy powder particles of small size, said alloy material having been subjected to a hardening and embrittling treatment, and thereafter decarburizing said alloy powder particles of small size to form a low coercive force alloy powder composed essentially oi large amounts of each of nickel and iron and a small amount of molybdenum, said low coercive force material containing not more than .05% of carbon.

5. A method of forming a magnetic alloy powder of low coercive Iorce which comprises, forming a molten composition composed of iron, nickel, molybdenum and about 1 to 4% of carbon, atomizing said molten composition and rapidly cooling the same by flowing a stream of the molten composition into a high velocity jet oi water to form comparatively hard and brittle particles of rather small size, comminuting said brittle atomized alloy powder particles to form an alloy powder of a size such that it will substantially all pass through a mesh screen and decarburizing said powder particles in a decarburizing, non-oxidizing atmosphere until the carbon content thereof is not greater than .05%.

6. A method of forming a low coercive force alloy powder which comprises iorming a molter composition consisting of about 48% nickel, about 2.40% molybdenum, about 2% carbon and the balance substantially all iron, atomizing saic' material and rapidly cooling the same to form comparatively hard and brittle particles, comminuting said brittle particles to form powdei particles of a desired size and shape, and decarburizing said powder particles to form a low coercive force alloy powder composed essential]: of nickel, molybdenum and iron.

'7. A method of making a low coercive Iorcq alloy powder adapted to be briquetted and sintered to form relay cores and the like whicl comprises, comminuting an alloy material com posed of about 48% nickel, about 2.40% molyb denum, about 2% carbon, and the balance lIOl .plus traces ocf non-essential impurities to torn powder particles, and decarburizing said powde particles to form a low coercive force alloy pow der composed essentially of nickel, molybdenun and iron.

8. The method of 'making a strong, homogene ous sintered relay core and the like which com prises, treating an alloy containing a large pro portion of each of nickel and iron and contain ing about 1 to 4% of carbon, to make it rela tively hard and brittle, said alloy when substan tially devoid of carbon being one of low coercive force, comminuting said treated alloy to form a fine powder, and decarburizing the alloy powder toform a low coercive force powder containing large amounts of each of nickel and iron and containing no more than .05% of carbon, briquetting the powder of low coercive force to form a, relay core, and sintering said briquette under non-oxidizing conditions to form a strong relay core of homogeneous structure.

9. A method as in claim 5 in which the molten composition contains about 48% nickel, about 2.00-2.50% molybdenum, about 2 to 4% of carhem and the balance substantially all iron.

ALFRED L. BOEGEHOLD. 

